Manufacturing facilities produce useful articles by processing component into finished goods. The operations used to process the components may involve transformational steps that change the article from one state to another. Some of these transformational operations employ machinery, such as presses, cutting tools, conveyor systems, ovens, or chemical applicators, for example.
Some manufacturing facilities use machinery that can be dangerous to humans. For example, a worker who walks into a zone of operation of a large robotic arm is at risk of serious bodily harm if the arm's motion profile intersects the worker's body or clothing. In another example, a worker who places a work piece in a press and reaches into the press while the press is activated could be severely injured.
To promote safety for operators and machines, many manufacturing machines are protected, either partially or entirely surrounded by light curtain systems. A light curtain safety system may cause a machine to be deactivated when an object interrupts any portion of the light curtain. For example, a hand extending through the light curtain may block one or more beams of the light curtain, which the light curtain may interpret as a potential danger condition. The light curtain may typically respond by causing the machine to be deactivated by, for example, engaging a braking system and/or interrupting electric power to motor drives that cause a press to move. A light curtain safety system may also prevent a machine from being activated when an object is present in any portion of the light curtain. For example, prior to machine startup, an operator who is standing too close, or within hazardous proximity, to a machine may block one or more beams of the light curtain. The light curtain may interpret this as a danger condition and prevent machine startup.
In some installations protected by a light curtain system, it may be desirable to program the system to permit machinery to continue to run even in the presence of certain beams being blocked. In some instances, this ability to continue to run protected machinery while selected beams are being blocked is called “fixed blanking” In a fixed blanking implementation, the system will not shut off the protected equipment just because certain optical beams are blocked. Thus, a fixed blanking function allows a protected system to be programmed to continue to run even while some object (e.g., a shelf, conveyor belt, or other stationary object) is blocking certain selected optical beams in the light curtain system.